The present invention relates to a sliding gate mechanism for a bottom pouring vessel used for the storage, transport and dispensing of molten materials such as liquid metals.
In such devices, such as casting ladles or tundish pouring systems, the flow of molten metal from the vessel is controlled by a sliding gate mechanism. Such mechanisms typically consist of a series of shutter plates having orifices or holes therethrough. The plates are attached under the vessel such that the plates may be displaced with respect to each other thereby aligning or misaligning the orifices. This allows the liquid metal to flow from the vessel at a rate dependent upon the degree of coaxial alignment of the orifices.
Sliding gate valve systems have been successfully used to control molten metal flow from containing vessels for several years. Examples of typical sliding gate valve systems can be found in U.S. Pat. No. 3,918,613 to Shapland and U.S. Pat. No. 3,581,948 to Detalle.
There are numerous advantages associated with using a sliding gate mechanism for pouring molten metals as compared to other flow-controlling mechanisms such as those using a stopper and an associated stopper rod. The absence of the stopper rod mechanism leading out of the container makes the slide gate pouring system particularly useful in vacuum or continuous casting. The sliding gate system, being outside the containing vessel, is less susceptible to the damaging effects of metal temperatures, chemical attack from molten slag and metal erosion. In addition, the sliding gate system more effectively controls molten metal flow by controlling the degree of coaxial alignment of the orifices in the sliding plates.
Conventionally, sliding gate mechanisms include a prefired refractory plate which is assembled into a metal-supporting can after firing. The refractory/metal assembly is securely attached to the bottom of the vessel containing molten metal. Another refractory/metal assembly is matched to the first such that the degree of coaxial alignment of the orifices in the refractory plates will control the rate of molten metal flow from the vessel, through the sliding gate mechanism and into the appropriate mold. In order to insure an effective seal between the refractory plates in the sliding gate mechanism, the mating surfaces of the prefired refractory plates are precision ground before they are attached to the containing vessel. This grinding operation normally occurs after the refractory is assembled into the supporting can, but the grinding operation may also be carried out prior to the assembly of the refractory into the metal can.
The actual manufacture and assembly of the precision ground refractory is critical to the successful operation of the sliding gate system. A key element in this operation is the assembly of the prefired refractory plate and its supporting metal can. The bond between the refractory and the metal can is crucial. Weak bonds between the refractory and the metal can cause the refractory plate to wobble or shift within the metal can. This shifting hampers efforts to obtain a precision ground surface on the matching faces of the refractories necessary to form an effective seal. If an effective seal cannot be formed, the entire assembly must be scrapped. In addition, if weak bonds are not discovered during assembly or during the grinding operation and the assembly is used to control the molten metal flow in a containing vessel, the refractory plate may shift when the sliding gate mechanism is used. The shifting may hamper the closing of the valve, causing leaks and, in general, may create a dangerous situation for operating personnel.
Currently, refractory/metal assemblies of the prior art are produced by pressing a prefired refractory plate into a preformed metal can using a refractory mortar as the bonding medium. In order to accomplish this operation, the refractory mortar must be fluid enough to flow around the refractory plate during pressing such that the space (usually 1/8-1/4 inch) between the plate and the metal can is filled with mortar. A mortar with sufficient fluidity to fill this space undergoes considerable shrinkage upon firing. Assemblies made in this manner exhibit significant amounts of separation between the metal can and the refractory plate where the mortar has shrunk from the metal can. This type of bonding is dependent on the mechanical locking associated with flaws or irregularities in the metal can. This means of locking the refractory plate to the metal can is unsatisfactory and refractory plates have been known to separate totally from the metal can and fall out of the assembly.
Another disadvantage of the prior art method of assembling the refractory in the metal can is the pressing operation. The pressing of prefired refractory plates that are slightly warped, flawed or dimensionally inaccurate can cause damage to the part which, in turn, causes the assembly to be scrapped. Even if the refractory plate is dimensionally correct, if it is pressed in a metal can containing too thick or too stiff a mortar, or if there is an improper distribution of this stiff mortar in the metal can, the refractory plate or the metal can will be damaged by the pressing operation.
Still another disadvantage of this prior art assembly method is that uneven distribution of mortar between refractory plate and metal can can develop uneven stress distributions in the assembly. During the grinding operation, this may cause cracking of the refractory plate.
Yet another disadvantage of this operation is that the layer of mortar between refractory plate and metal can is necessarily thin. This precludes the use of mechanical locks between metal can and mortar such as metal pins, which could extend from the metal can into the mortar layer. A system using mechanical interlocking means would require a relatively thick mortar layer. This would only aggravate shrinkage and mortar distribution problems.
Still another disadvantage of the prior art method of assembling the refractory in the metal can is the result of using prefired refractory plates. These plates are relatively difficult to manufacture and their manufacture entails a considerable cost in energy resources and manpower. Refractory shapes which are off-size, warped, chipped, or cracked must be scrapped, which significantly adds to the cost of the finished product. The finished refractory plates are themselves brittle and easily damaged during shipping, handling and the assembly operation. Damage to the correctly manufactured refractory plates adds still more to their final cost.
Yet another disadvantage of the prior art products is the expense of the manufacturing method. The prefired refractory plates that are bonded to the metal cans are made of refractory mixes which are pressed, low fired and then high fired. These prefired refractory plates are then pressed into the metal can with refractory mortar and then refired at low temperature, usually about 600.degree. F. The elimination of the second pressing operation and the associated low firing step, as well as the elimination of the high firing step, would considerably reduce the consumption of energy and the ultimate cost of the product.
The present invention is more economical to manufacture but produces a better product. It also results in safer operation of the vessels dispensing molten metal with slide gate valves.
Additional advantages will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the combinations particularly pointed out in the appended claims.